EP0844628A1 - Process for producing a magnetic core of nanocristalline soft magnetic material - Google Patents

Abstract

Production of a magnetic core of soft magnetic iron-based alloy having a nanocrystalline structure involves determining the annealing temperature (Tm) required, for an amorphous ribbon of the alloy, to achieve maximum magnetic permeability and subjecting a core blank, produced from an amorphous ribbon of the alloy, to annealing at 20-50 (preferably 20-40) degrees C above Tm for 0.1-10 (preferably 0.5-5) hrs. to cause nanocrystal formation. The alloy has the composition (in atomic %) ≥ 60% Fe, 0.1-3% (preferably 0.5-1.5) Cu, 0-25% B, 0-30% (preferably 12-17) Si, 0.1-30% (preferably 2-5) one or more of Nb, W, Ta, Zr, Hf, Ti and Mo, and balance impurities, the sum of Si and B being 5-30% (preferably 15-25).

Description

The present invention relates to nanocrystalline magnetic materials intended, in particular, for the manufacture of magnetic circuits for apparatus electric.

Nanocrystalline magnetic materials are well known and have been described, in particular, in European patent applications EP 0 271 657 and EP 0 299 498. These are iron-based alloys, containing more than 60 at% (atoms%) of iron, copper, silicon, boron, and possibly at least one element taken among niobium, tungsten, tantalum, zirconium, hafnium, titanium and molybdenum, cast in the form of amorphous ribbons and then subjected to a treatment which causes extremely fine crystallization (the crystals have less 100 nanometers in diameter). These materials have magnetic properties particularly suitable for the manufacture of soft magnetic cores for electrotechnical devices such as earth leakage circuit breakers. In particular, they have excellent magnetic permeability and can exhibit either a cycle round hysteresis (Br / Bm ≥ 0.5), i.e. a cycle of coated hysteresis (Br / Bm ≤ 0.3); Br / Bm being the ratio of remanent magnetic induction to magnetic induction maximum. Round hysteresis cycles are obtained when treatment thermal consists of a simple annealing at a temperature of about 500 ° C. The lying hysteresis cycles are obtained when the heat treatment involves at least one annealing under magnetic field, this annealing being able to be the annealing intended to cause the formation of nanocrystals.

Materials with a round hysteresis cycle may exhibit very high magnetic permeability, even higher than that of alloys of the type Classic permalloys. This very high magnetic permeability makes them, a priori, particularly suitable for the manufacture of magnetic cores for circuit breakers AC class differentials, i.e. sensitive to fault currents alternative. However, for such use to be possible, it is necessary that the magnetic properties of the nuclei are sufficiently reproducible to that mass production is satisfactory.

To mass produce magnetic cores for earth leakage circuit breakers of class AC, an amorphous magnetic alloy ribbon capable of being used to acquire a nanocrystalline structure. We make a series of section tori substantially rectangular by winding a certain length of ribbon on a mandrel and by making a solder point. The toroids thus obtained are then annealed in order to cause the formation of nanocrystals and, as a result, their confer the desired magnetic properties. The annealing temperature, which located around 500 ° C, is chosen so that the magnetic permeability of the alloy is maximum. The magnetic cores thus obtained are intended for receive windings which generate mechanical stresses which deteriorate the magnetic properties of the nuclei. To limit the consequences of winding stresses, the toroids are arranged in protective boxes with the interior of which they are wedged for example by foam rings. However, this wedging of the toroids in their casing induces, by itself, low stresses which are detrimental to the excellent magnetic properties developed on the nucleus. The use of a protective case although effective not always sufficient, and, after winding, the properties of the devices obtained by industrial production are degraded and too dispersed to be even acceptable for the intended use.

The object of the present invention is to remedy these drawbacks by proposing a means for mass production of magnetic cores of material nanocrystalline, having both magnetic permeability (relative permeability impedance at 50 Hz maximum) greater than 400,000 and a round hysteresis cycle, so that the dispersion of their magnetic properties is compatible with the use for mass production of class GFCIs AC.

• on fabrique avec l'alliage magnétique un ruban amorphe,
• on détermine la température Tm de recuit qui, pour le ruban, conduit à la perméabilité magnétique maximale,
• avec le ruban on fabrique au moins une ébauche de noyau,
• et on soumet l'au moins une ébauche de noyau à au moins un recuit effectué à une température T comprise entre Tm + 10°C et Tm + 50°C, et de préférence, entre Tm + 20°C et Tm + 40°C, pendant un temps de maintien t compris entre 0,1 et 10 heures, et de préférence, entre 0,5 et 5 heures, afin de provoquer la formation de nanocristaux. Au moins un recuit peut être effectué sous champ magnétique.

To this end, the subject of the invention is a process for manufacturing at least one magnetic core made of a soft iron-based magnetic alloy having a nanocrystalline structure, according to which:

• an amorphous ribbon is made with the magnetic alloy,
• the annealing temperature Tm is determined which, for the ribbon, leads to the maximum magnetic permeability,
• with the ribbon at least one core blank is made,
• and at least one core blank is subjected to at least one annealing carried out at a temperature T of between Tm + 10 ° C and Tm + 50 ° C, and preferably between Tm + 20 ° C and Tm + 40 ° C, for a holding time t of between 0.1 and 10 hours, and preferably between 0.5 and 5 hours, in order to cause the formation of nanocrystals. At least one annealing can be carried out under magnetic field.

This process applies to all soft magnetic alloys based on iron capable of exhibiting a nanocrystalline structure, and more particularly to alloys whose chemical composition comprises, in% atoms: Fe ≥ 60% 0.5% ≤ Cu ≤ 1.5% 5% ≤ B ≤ 14% 5% ≤ Si + B ≤ 30% 2% ≤ Nb ≤ 4%

The invention will now be described in more detail, but not in detail. limiting and illustrated by an example.

• de 0,1 à 3 at %, et de préférence, de 0,5 à 1,5 at % de cuivre ;
• de 0,1 à 30 at %, et, de préférence, de 2 à 5 at % d'au moins un élément pris parmi le niobium, le tungstène, le tantale, le zirconium, le hafnium, le titane, et le molybdène ; de préférence, la teneur en niobium est comprise entre 2 et 4 at % ;
• du silicium et du bore, la somme des teneurs en ces éléments étant comprise entre 5 et 30 at %, et, de préférence, entre 15 et 25 at % ; la teneur en bore pouvant aller jusqu'à 25 at %, et, de préférence, étant comprise entre 5 et 14 at % ; la teneur en silicium pouvant atteindre 30 at %, et, de préférence, étant comprise entre 12 et 17 at %.

To mass produce magnetic cores for differential circuit breakers of class AC (sensitive to alternating fault currents), a ribbon of soft magnetic alloy having an amorphous structure is used, capable of acquiring a nanocrystalline structure, mainly consisting of iron in one content greater than 60 atom%, and also containing:

• 0.1 to 3 at%, and preferably 0.5 to 1.5 at% copper;
• from 0.1 to 30 at%, and preferably from 2 to 5 at% of at least one element chosen from niobium, tungsten, tantalum, zirconium, hafnium, titanium, and molybdenum; preferably, the niobium content is between 2 and 4 at%;
• silicon and boron, the sum of the contents of these elements being between 5 and 30 at%, and preferably between 15 and 25 at%; the boron content which can range up to 25 at%, and preferably being between 5 and 14 at%; the silicon content being able to reach 30 at%, and preferably being between 12 and 17 at%.

The chemical composition of the alloy may also include low contents of impurities provided by raw materials or resulting from development.

The amorphous ribbon is obtained in a manner known per se by solidification very fast liquid alloy. Magnetic core blanks are fabricated also in a manner known per se by winding the ribbon on a mandrel, cutting it and fixing its end with a welding point, in order to obtain small tori of rectangular section. The blanks must then be subjected to a annealing treatment to precipitate nanocrystals in the amorphous matrix of size less than 100 nanometers. This very fine crystallization makes it possible to obtain desired magnetic properties, and thus transforming the core blank magnetic in magnetic core.

The inventors having unexpectedly found that the effect of the conditions annealing on the magnetic properties of the nuclei depended not only on the chemical composition of the alloy, but also, and not very controllably, special manufacturing conditions for each ribbon taken individually, before to carry out the annealing, the temperature Tm which determines, for an annealing of given duration, at the maximum magnetic permeability that it is possible to obtain on a torus made with the ribbon. This temperature Tm is specific to each ribbon, it is therefore determined for each ribbon by tests that a person skilled in the art can do.

After determining the temperature Tm, the annealing is carried out at a temperature T between Tm + 10 ° C and Tm + 50 ° C, and preferably between Tm + 20 ° C and Tm + 40 ° C, for a time between 0.1 and 10 hours, and, from preferably between 0.5 and 5 hours.

Temperature and time are two setting parameters for annealing partially equivalent. However, variations in the annealing temperature have a much stronger effect than variations in the duration of annealing, in particular at the ends of the admissible annealing temperature range. Also, the temperature is a relatively coarse adjustment parameter of the conditions of processing, time is a fine adjustment parameter.

The specific conditions of treatment are determined based on the intended use for the magnetic core.

After the heat treatment, each core is placed in a box protector, in which it is wedged, for example, with foam washers. For some applications, each core can be coated in a resin.

The annealing temperature is not equal to Tm, the magnetic permeability of nuclei is not maximum. However, the inventors have found that in doing so, one could obtain a sufficiently reliable permeability magnetic greater than 400,000. They also found that the nuclei obtained magnets were well suited for mass production of circuit breakers differentials, and, in particular, they were less sensitive to the effect of constraints winding.

As an example on the one hand, and for comparison on the other hand, three batches A, B and C of 200 geometrically identical toric magnetic cores were manufactured ( int = 11 mm,  ext = 15 mm, height = 10 mm). The three batches were produced with the alloy Fe ₇₃ Cu ₁ Nb ₃ Si ₁₅ B ₈ (in% atoms), cast in the form of an amorphous ribbon 22 µm thick. After manufacturing the magnetic core blanks, the temperature Tm was determined which was 500 ° C for 1 hour. Lot A was annealed at 505 ° C (Tm + 5 ° C) for 1 hour, in accordance with the prior art, lot B was annealed at 530 ° C (Tm + 30 ° C) for 3 hours, in accordance with the prior art to the invention, and batch C was annealed at 555 ° C (Tm + 55 ° C) for 3 hours, for comparison. The mean and standard deviation of the magnetic permeability values were determined for each of the batches, on the one hand for the naked nuclei, and on the other hand for the cased nuclei, that is to say, subjected to light stresses due to the setting of the torus in its case. The results of the set of measurements were as follows (in the three cases, the Br / Bm ratio was approximately 0.5): Naked core Core in housing Average Standard deviation Average Standard deviation AT 550,000 100,000 480,000 120,000 B 490,000 70,000 490,000 70,000 VS 360,000 70,000 360,000 70,000

These results show that, contrary to what is observed for lot A, the average of the magnetic permeability values of the nuclei of lot B is little affected by the packaging and the constraints it generates. So is even for lot C. However, while the average permeability values magnetic magnetic cores in the housing of lots A and B are comparable, the mean of the magnetic permeability values of the magnetic cores under case of lot C is significantly lower.

We also note that the standard deviations of the permeability values magnetic magnetic cores, in a case or not, lots B and C are more lower than the standard deviation of the magnetic permeability values of the nuclei magnetic, in case or not, of lot A. The difference between lots A and B results that the magnetic cores in lot B are less sensitive to stresses mechanical than the magnetic cores in lot A. The magnetic cores in lot C are a priori less sensitive to mechanical stresses than cores magnetic of batch B, but have permeabilities incompatible with the application.

It results from differences between the means on the one hand, and the standard deviations on the other hand, that about 23% of the nuclei of lot A and about 80% of the nuclei of lot C have a magnetic permeability of less than 400,000, while only 13% lot B cores have a magnetic permeability of less than 400,000.

Furthermore, because the dispersion of the magnetic properties of the nuclei of batch B is lower than that of the nuclei of batch A, and because the sensitivity of these properties under mechanical stress is lower for lot B than for lot A, after winding the magnetic cores of lot B are well suited to use in class AC residual current devices, while the cores of the lot A are not reliably so. The magnetic cores of lot C, although having theoretically lower sensitivity to mechanical stresses than lot B cores, are not suitable for use in circuit breakers differentials, especially because they have insufficient magnetic permeability.

For certain applications (for example earth leakage circuit breakers class A), it is necessary to use magnetic cores with cycles lying hysteresis. Such cores can be made by performing at least annealing under magnetic field. Annealing under magnetic field can be either the annealing which has just been described and which is intended to cause the precipitation of nanocrystals, i.e. an additional annealing carried out between 350 and 550 ° C. The cores thus obtained have, in the same way, a sensitivity to the stresses very low mechanical properties, which increases the reliability of mass production.

Claims (10)

Method for manufacturing at least one magnetic core made of a soft magnetic alloy based on iron having a nanocrystalline structure characterized in that: an amorphous ribbon is made with the magnetic alloy, the annealing temperature Tm is determined which, for the strip, leads to the maximum magnetic permeability, with the ribbon at least one core blank is made, and the at least one core blank is subjected to at least one annealing, the said annealing being carried out at a temperature T of between Tm + 10 ° C and Tm + 50 ° C for a holding time t of between 0.1 and 10 hours, in order to cause the formation of nanocrystals. Method according to claim 1 characterized in that the time of maintenance is between 0.5 and 5 hours. Method according to claim 1 characterized in that the temperature T annealing is between Tm + 20 ° C and Tm + 40 ° C. Process according to any one of Claims 1 to 3, characterized in that the chemical composition of the soft iron-based magnetic alloy comprises, in% atoms: Fe ≥ 60% 0.1% ≤ Cu ≤ 3% 0% ≤ B ≤ 25% 0% ≤ If ≤ 30% at least one element taken from niobium, tungsten, tantalum, zirconium, hafnium, titanium, and molybdenum in contents of between 0.1% and 30%, the rest being impurities resulting from the production , the composition also satisfying the relationships: 5% ≤ Si + B ≤ 30% Process according to Claim 4, characterized in that the chemical composition of the soft iron-based magnetic alloy is such that: 15% ≤ Si + B ≤ 25% Process according to Claim 4, characterized in that the chemical composition of the soft iron-based magnetic alloy is such that: 0.5% ≤ Cu ≤ 1.5% Method according to claim 4 characterized in that the composition chemical of the soft iron base magnetic alloy is such that it contains at least one element taken from niobium, tungsten, tantalum, zirconium, hafnium, titanium, and molybdenum in a content of between 2% and 5%. Process according to Claim 4, characterized in that the chemical composition of the soft iron-based magnetic alloy is such that: 12% ≤ If ≤ 17% Process according to Claim 8, characterized in that the chemical composition of the soft iron-based magnetic alloy is such that: 0.5% ≤ Cu ≤ 1.5% 5% ≤ B ≤ 14% 15% ≤ Si + B ≤ 25% and the content of at least one element chosen from niobium, tungsten, tantalum, zirconium, hafnium, titanium, and molybdenum is between 2% and 4%. Method according to claim 1 characterized in that at least one annealing is carried out under magnetic field.